NFC-Enabled Constrained Device, NFC-Enabled Control Device, and Method Thereof

ABSTRACT

A Near-Field Communication (NFC)-enabled constrained device (100) is provided. The constrained device (100) comprises a processing circuit (111) operative to implement a functionality of the constrained device (100), an NFC-interface circuit (115) configured to harvest power transmitted by an NFC-enabled control device (200) and to enable exchange of data with the control device (200), when the devices are in proximity, and a restart circuit (121) configured to accumulate electrical charge using the harvested power received from the NFC-interface circuit (115), and to trigger restart of the processing circuit (111) when the accumulated electrical charge exceeds a threshold level. Further provided is an NFC-enabled control device (200) for restarting the NFC-enabled constrained device (100). The control device (200) comprises an NFC-interface circuit (215) configured to transmit power to the constrained device (100) and to enable exchange of data with the constrained device (100), when the devices are in proximity, and a processing circuit (211) operative to initiate the transmission of power to the constrained device (100), and to control the exchange of data with the constrained device (100).

TECHNICAL FIELD

The invention relates to a Near-Field Communication (NFC)-enabledconstrained device, an NFC-enabled control device for restarting anNFC-enabled constrained device, a method of restarting an NFC-enabledconstrained device, a corresponding computer program, and acorresponding computer program product.

BACKGROUND

Many types of Internet-of-Things (IoT) devices, such as sensors andactuators, are characterized by their small size and limitedcapabilities, especially with respect to their processing power andbattery capacity. These types of devices are sometimes referred to asconstrained devices (see, e.g., “Terminology for Constrained-NodeNetworks”, Request for Comments (RFC) 7228, Internet Engineering TaskForce (IETF), May 2014).

A common constraint of IoT devices and other types of constraint devicesrelates to limitations in user interfaces and accessibility duringdeployment and operation, e.g., for data exchange with the IoT device,configuration changes or software update of the IoT device, restart ofthe IoT device, and so forth. In order to reduce size and complexity,many IoT devices such as sensors are only equipped with an NFC interfacefor exchange of data, and do not comprise any keys, buttons, or othermeans which enable a human user to control the IoT device. In addition,such devices are oftentimes provided with integrated, non-removablebatteries. As an example, sensor devices, such as blood glucose sensorswhich are worn on a person's skin or may even be implanted into aperson's body, typically comprise a battery-powered processor operativeto periodically read-out measured data from a sensor and store themeasured data in a memory. The stored data can subsequently be read-outvia the NFC interface by using an NFC control device, such as anNFC-enabled smartphone using a dedicated software application or app.

In addition to exchanging data with the sensor device, the controldevice can transmit power over the NFC interface, which power can beharvested by the sensor device, e.g., for use as power supply for theNFC-interface circuit of the sensor device or for charging the sensor'sbattery. In NFC terminology, this type of devices is referred to as asemi-passive tag operating in NFC reader/writer mode.

An inherent problem of constrained devices, in particular those whichonly comprise an NFC interface but no additional interface such as abuttons or keys, is the difficulty to restart, or reset, the device, ifthe device has become non-operational. This may, e.g., be the case if aprocessor implementing the device's functionality (such as periodicallyreading-out and storing sensor data for later read-out) by executing asoftware has become non-operational (i.e., has “crashed”) due to amalfunction (“bug”) of the software. Alternatively, if the processorcomprises an Application-Specific Integrated Circuit (ASIC), a FieldProgrammable Gate Array (FPGA), a Complex Programmable Logic Device(CPLD), or similar type of circuit, a design-flaw in the processor'sstate machine may result in the processor reaching an inescapable stateand the device accordingly becoming non-operational.

In situations when a constrained device has become non-operational, itmay become unresponsive to restart or reset commands which are receivedvia the device's NFC interface. Since no keys or buttons for triggeringa restart or reset by manual user interaction are available, and thebattery cannot be removed to force a cold reset, the constrained devicemay need to be replaced.

SUMMARY

It is an object of the invention to provide an improved alternative tothe above techniques and prior art.

More specifically, it is an object of the invention to provide animproved solution for restarting NFC-enabled constrained devices.

These and other objects of the invention are achieved by means ofdifferent aspects of the invention, as defined by the independentclaims. Embodiments of the invention are characterized by the dependentclaims.

According to a first aspect of the invention, an NFC-enabled constraineddevice is provided. The constrained device comprises a processingcircuit operative to implement a functionality of the constraineddevice, an NFC-interface circuit, and a restart circuit. TheNFC-interface circuit is configured to harvest power transmitted by anNFC-enabled control device and to enable exchange of data with thecontrol device, when the constrained device and the control device arein proximity. The restart circuit is configured to accumulate electricalcharge using the harvested power received from the NFC-interfacecircuit, and to trigger restart of the processing circuit when theaccumulated electrical charge exceeds a threshold level.

According to a second aspect of the invention, an NFC-enabled controldevice for restarting an NFC-enabled constrained device is provided. Thecontrol device comprises an NFC-interface circuit and a processingcircuit. The NFC-interface circuit is configured to transmit power tothe constrained device and to enable exchange of data with theconstrained device, when the constrained device and the control deviceare in proximity. The processing circuit is operative to initiate thetransmission of power via the NFC-interface circuit to the constraineddevice, and to control the exchange of data with the constrained devicevia the NFC-interface circuit.

According to a third aspect of the invention, a method of restarting anNFC-enabled constrained device is provided. The method is performed byan NFC-enabled control device comprising an NFC-interface circuitconfigured to transmit power to the constrained device and to enableexchange of data with the constrained device, when the constraineddevice and the control device are in proximity. The method comprisesinitiating the transmission of power via the NFC-interface circuit tothe constrained device, and controlling the exchange of data with theconstrained device via the NFC-interface circuit.

According to a fourth aspect of the invention, a computer program isprovided. The computer program comprises computer-executableinstructions for causing an NFC-enabled control device to perform themethod according to an embodiment of the third aspect of the invention,when the computer-executable instructions are executed on one or moreprocessors comprised in the control device.

According to a fifth aspect of the invention, a computer program productis provided. The computer program product comprises a computer-readablestorage medium which has the computer program according to the fourthaspect of the invention embodied therein.

The invention makes use of an understanding that NFC-enabled constraineddevices which have become non-operational may be restarted by utilizingthe power which is transmitted from the NFC-enabled control device tothe constrained device, where it is harvested, when the two devices arein proximity. Embodiments of the invention are advantageous in that therestart of the processor circuit comprised in the constrained device,which implements the functionality of the constrained device, isachieved by means of a relatively simple electronic circuit which doesnot rely on any data exchange with the control device, such as receivinga reset signal or request via the NFC interface, but on accumulatingcharge until a threshold level is exceeded.

Even though advantages of the invention have in some cases beendescribed with reference to embodiments of the first and second aspectsof the invention, corresponding reasoning applies to embodiments ofother aspects of the invention.

Further objectives of, features of, and advantages with, the inventionwill become apparent when studying the following detailed disclosure,the drawings and the appended claims. Those skilled in the art realizethat different features of the invention can be combined to createembodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of theinvention, will be better understood through the following illustrativeand non-limiting detailed description of embodiments of the invention,with reference to the appended drawings, in which:

FIG. 1 schematically illustrates an NFC-enabled constrained device andan NFC-enabled control device, in accordance with embodiments of theinvention.

FIG. 2 illustrates an embodiment of the restart circuit, implementing asingle threshold voltage level for triggering restart of the processingcircuit.

FIG. 3 illustrates another embodiment of the restart circuit,implementing different threshold voltage levels for separatelytriggering restart of a plurality of processing circuit modulescomprised in the processing circuit.

FIG. 4 shows a method performed by the NFC-enabled control device, inaccordance with embodiments of the invention.

All the figures are schematic, not necessarily to scale, and generallyonly show parts which are necessary in order to elucidate the invention,wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

The invention will now be described more fully herein after withreference to the accompanying drawings, in which certain embodiments ofthe invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided byway of example so that this disclosure will be thorough and complete,and will fully convey the scope of the invention to those skilled in theart.

In FIG. 1 a Near-Field Communication (NFC)-enabled constrained device100 and an NFC-enabled control device 200 are illustrated, in accordancewith embodiments of the invention.

In the present context, a constrained device is understood to be acomputing device with comparatively limited capabilities in terms ofprocessing power and battery capacity, and may also be limited withrespect to the number and type(s) of interfaces for accessing, orinteracting with, the constrained device, such asdata/communication/network interfaces, keys, buttons, displays, hapticsensors and actuators, microphones, loudspeakers, and the like. Typicalexamples of this class of electronic devices are, e.g., IoT devices suchas sensors and actuators. The solutions described herein address aproblem which is inherent to constrained devices which comprise sometype of processing circuit which implements a functionality provided bythe constrained device, and an NFC interface for accessing theconstrained device.

In NFC terminology, the NFC-enabled constrained device 100 may bereferred to as an “NFC tag” operating in semi-passive mode. Insemi-passive mode, also known as battery-assisted mode, such a deviceoperates stand-alone to perform a certain functionally which isimplemented by its battery-powered processing circuit. Thisfunctionality may, e.g., relate to applications which require autonomousand continuous monitoring, such as data loggers or medical sensors. AnNFC-enabled constrained device may harvest power which is transmitted byan NFC-enabled control device, also known as “NFC reader/writer” in NFCterminology, which is brought into proximity of the NFC-enabledconstrained device, within a distance of a few centimeters or shorter.The harvested power may be used to power the NFC-interface circuit ofthe NFC-enabled constrained device, effect data exchange with thecontrol device, and/or charge the battery of the NFC-enabled constraineddevice.

Further with reference to FIG. 1, the NFC-enabled constrained device 100comprises a processing circuit 111 which is operative to implement afunctionality of the constrained device 100, and an NFC-interfacecircuit 115. The NFC-interface circuit 115 is configured to harvestpower which is transmitted by the NFC-enabled control device 200 and toenable exchange of data with the control device 200. The transmissionand harvesting of power, as well as the exchange of data, via the NFCair-interface can commence when the constrained device 100 and thecontrol device 200 are brought into proximity, typically within adistance of a few centimeters or shorter. Exchange of data is to beunderstood to encompass transmission of data from the NFC-enabledcontrol device 200 to the NFC-enabled constrained device 100, and/orvice versa, using any suitable communications protocol and data format,or a combination of suitable communications protocols and/or dataformats.

The NFC-enabled constrained device 100 further comprises a restartcircuit 121 which is configured to accumulate electrical charge usingthe harvested power received from the NFC-interface circuit 115 (viaconnection 122), and to trigger restart of the processing circuit 111(via connection 123) when the electrical charge accumulated by therestart circuit 121 exceeds a threshold level. Throughout thisdisclosure, the terms “restart” and “reset” are used interchangeably.

As is illustrated in FIG. 1, the restart of the processing circuit 111is triggered via connection 123 to a reset input which the processingcircuit 111 is provided with. Most commercially available processingcircuits are provided with a reset input which, when set to a definedvoltage level such as low (“0”) or high (“1”), initiates a reset of theprocessing circuit in a controlled manner.

The processing circuit 111 may comprise one or more processors, e.g.,any type of general-purpose Central Processing Unit (CPU),microprocessor, System-on-Chip (SoC), Graphics Processing Unit (GPU),Digital Signal Processor (DSP), or the like, operative to executecomputer-readable instructions 113, i.e., software, which are stored ina memory 112 comprised in the processing circuit 111, and which causethe processing circuit 111 to implement the functionality of theconstrained device 100. In general, computing devices which providefunctionality implemented by software which is executed by a one or moreprocessors are prone to malfunction or design flaws of the software (aka“bugs”) which may result in the computing device becomingnon-operational (which is commonly referred to as a “crash” of thecomputing device). The memory 112 may, e.g., be a Random-Access Memory(RAM), a Read-Only Memory (ROM), a Flash memory, or the like.

Alternatively, the processing circuit 111 may comprise one or more of anASIC, an FPGA, and a CPLD. In such circuits, a design-flaw in theprocessing circuit's state machine may result in the processing circuitreaching an inescapable state, and the device accordingly becomingnon-operational.

The processing circuit 111 may be powered by a battery 116 which iscomprised in the constrained device. Typically, due to size limitationsof constrained devices, and to reduce complexity and manufacturingcosts, the battery 116 is non-removable. Consequently, the constraineddevice cannot be restarted by removing or disconnecting the battery (aka“cold restart”).

The constrained device 100 may optionally be configured to be accessibleexclusively through data exchanged via the NFC-interface circuit 115. Insuch scenario, which is typical for constrained device, the constraineddevice does not have any other interface(s) for data exchange orinteraction with a human user, such as keys or buttons for resetting theconstrained device. This means that the constrained device 100 isaccessible by transmitting data to the constrained device 100 via theNFC-interface circuit 115, such as requests or commands (e.g., a restartcommand), and/or receiving data from the constrained device 100 via theNFC-interface circuit 115, such as results of measurements performed bythe constrained device 100 or any other data.

As an example, the constrained device 100 may further comprise a sensor117, and the functionality of the constrained device 100 may comprisereading sensor data from the sensor 117, storing the sensor data 114 ina memory 112 comprised in the processing circuit 111 (or in a separatememory provided in the constrained device 100), and transmitting thesensor data 114 via the NFC-interface circuit 115 to the NFC-enabledcontrol device 200. In practice, the acquired and stored sensor data 114is transmitted by the constrained device 100 in response to receiving arequest from the control device 200. Alternatively, the constraineddevice 100 may be operative to transmit the acquired sensor data 114 inresponse to detecting proximity of the control device 200. This may,e.g., be achieved by detecting that a voltage of the harvested powerrises above a threshold level, after harvesting of power by theNFC-interface circuit 115 has commenced. As is illustrated in FIG. 1,the NFC-interface circuit 115 may be configured to directly retrieve thestored sensor data 114 from the memory 112 (via connection 131), or byoperation of the processing circuit 111 (via connection 132).

For instance, the constrained device 100 may be a sensor device, e.g., ablood glucose sensor which is worn on a person's skin or may even beimplanted into a person's body. Such sensors typically comprise abattery-powered processor which is operative to periodically read-outmeasured data from a blood-glucose sensor, and to store the measureddata in a memory. The stored data can subsequently be read-out via NFCby an NFC-enabled control device, such as an NFC-enabled smartphoneusing a dedicated software application or app.

As an alternative, the constrained device 100 may further comprise anactuator (not shown in FIG. 1), and the functionality of the constraineddevice 100 may comprise receiving a request or command, e.g., a signalor message, via the NFC-interface circuit 115 from the control device200, and activating the actuator in response to the received command. Asan example, the constrained device 100 may be an NFC-enabled electronicdoor lock which can be unlocked by an NFC-enabled smartphone 200 using adedicated software application or app. In such case, the command whichis received via the NFC-interface circuit 115 may comprise credentialslike a PIN code, a shared secret, a key, or a combination thereof.

The restart circuit 121 is configured to trigger restart of theprocessing circuit 111 after a duration of time, during which harvestedpower is received form the NFC-interface circuit 115, which issubstantially longer than a duration of time required for exchangingdata between the control device 200 and the constrained device 100during normal operation. More specifically, this is achieved by a properchoice of the time constant of the electronic circuit accumulating theelectrical charge which is received from the NFC-interface circuit 115,in the following referred to as charging circuit, in combination with aproper choice of the threshold level which, when exceeded, triggersrestart of the processing circuit 111. The time constant and thethreshold level are configured by design of the restart circuit 121.

As an example, if the duration of time which is required for exchangingdata between the control device 200 and the constrained device 100during normal operation is of the order of one second, or less, the timeconstant and the threshold level may be configured such that theduration of time during which harvested power is received form theNFC-interface circuit 115 is of the order of three to ten seconds.Selecting a duration of time during which harvested power is receivedform the NFC-interface circuit 115 which is substantially longer than aduration of time required for exchanging data between the control device200 and the constrained device 100 during normal operation isadvantageous in that unintentional restarts, which are triggered bymaintaining proximity between the constrained device 100 and the controldevice 200 for too long time, may be avoided.

An embodiment of the restart circuit 121 is illustrated in FIG. 2. Thetime constant of the charging circuit, i.e., the part of the restartcircuit 121 which accumulates the electrical charge which is receivedfrom the NFC-interface circuit 115, can be configured by proper designof the charging circuit and its electrical components. The chargingcircuit may, e.g., be implemented as a resistor-capacitor (RC) circuit.

For instance, if the charging circuit is a conventional first-order RCcircuit as illustrated in FIG. 2, comprising a resistor R₁ and acapacitor C, the voltage V_(C) over the capacitor C increases with timeas

V _(C) =V _(H)·(1−e ^(−t/(R) ¹ ^(·C)))   (1),

where V_(H) is the voltage of the harvested power received from theNFC-interface circuit 115 (via connection 122), and t is the time whichhas passed since the voltage V_(H) has been applied to the restartcircuit 121 (in practice, this is the time which has lapsed sinceharvesting of power by the NFC-interface circuit 115 has started and thevoltage V_(H) of the harvested power has reached stable value). The timeconstant of the first-order RC circuit is defined as

τ=R ₁ ·C   (2)

(with resistance R in Ω and capacitance C in Farads). A similar relationapplies to the charge Q accumulated by the capacitor C, as Q=V_(C)·C.Correspondingly, the charging current I_(R) through the resistor R₁decreases with time as

$\begin{matrix}{I_{R} = {\frac{V_{H}}{R_{1}} \cdot {e^{{- t}/{({R_{1} \cdot C})}}.}}} & (3)\end{matrix}$

In order to detect that the electrical charge accumulated by the restartcircuit 121, in particular by the capacitor C, exceeds a thresholdlevel, the restart circuit 121 may be configured to trigger restart ofthe processing circuit 111 when any one, or a combination of, thefollowing conditions are fulfilled: the charge which is accumulated bythe capacitor C rises above a threshold charge level, the voltage V_(C)which builds up over the capacitor C rises above a threshold voltagelevel, and the charging current I_(R) through the resistor R₁ fallsbelow a threshold current level.

As an example, and with reference to FIG. 2, the restart circuit 121 maycomprise a voltage comparator circuit which is configured to detect thatthe voltage V_(C) which builds up over the capacitor rises above athreshold voltage level V_(TH). Such a voltage comparator circuit may,e.g., comprise an operational amplifier (“OpAmp” in FIG. 2) which isarranged to compare the voltage V_(C) over the capacitor C, which isapplied to the non-inverting input of the operational amplifier (“+” inFIG. 2), to a reference voltage which is applied to the inverting input(“−” in FIG. 2) of the operational amplifier (for the sake ofsimplicity, the power supply inputs of the operational amplifier areomitted in FIGS. 2 and 3). The reference voltage is provided by means ofa voltage divider made up of R₂ and R₃, and defines the thresholdvoltage level,

$\begin{matrix}{V_{TH} = {V_{H} \cdot {\frac{R_{2}}{R_{2} + R_{3}}.}}} & (4)\end{matrix}$

While the voltage over the capacitor, V_(C), exceeds the thresholdvoltage level V_(TH), the output of the operational amplifier assumesthe higher level of the supply voltage of the operational amplifier(e.g., V_(H), or a voltage of the battery 116, if the restart circuit121 is powered by the battery 116), and while V_(C) does not exceedV_(TH) the output of the operational amplifier assumes the lower levelof the supply voltage (e.g., 0 V). It will be appreciated that theresistor R₂ may alternatively be connected to the voltage provided bythe battery 116, instead of the voltage V_(H) as illustrated in FIG. 2,in which case Eq. (4) is modified accordingly.

In the following, configuration of the restart circuit 121 in accordancewith embodiments of the invention is exemplified, for embodiments of theconstrained device 100 with rely on a the restart circuit 121 which isconfigured as to trigger restart of the processing circuit 111 when thevoltage V_(C) which builds up over the capacitor C rises above thethreshold voltage level V_(TH). To this end, based on Eqs. (1) and (2),it is known that the voltage over the capacitor V_(C) reaches a level of0.63·V_(H) after a time t which is equal to the time constant τ. Inorder to trigger restart of the processing circuit 111 when the voltageV_(C) exceeds the threshold voltage level V_(TH) of 0.63·V_(H), theresistors R₂ and R₃ which make up the voltage divider of the comparatorcircuit are dimensioned according to Eq. (4). More specifically, R₂ andR₃ are dimensioned such that R₂/(R₂+R₃) equals 0.63. This may, e.g., beachieved by using R₂ equal to 3.7 kΩ and R₃ equal to 6.3 kΩ. Further, inorder to configure the first-order RC circuit illustrated in FIG. 2 witha time constant τ of a desired value, R₁ and C are dimensioned inaccordance with Eq. (2). As an example, for a desired time constant τ ofthree seconds (3 s), the capacitor C may be dimensioned with 100 μF andthe resistor R₁ with 30 kΩ. It will be appreciated that the electroniccomponents comprised in the restart circuit 121 may be dimensioned in adifferent manner than what is exemplified hereinbefore, based on Eqs.(1), (2), and (4). It will also be appreciated that embodiments of theconstrained device 100 may alternatively rely on a restart circuit 121comprising a comparator circuit which is configured to detect that thecharge which is accumulated by the capacitor C rises above a thresholdcharge level, or that the charging current I_(R) through the resistor R₁falls below a threshold current level. As yet a further alternative,embodiments of the constrained device 100 may rely on a combination ofcomparator circuits of different types, wherein the restart circuit 121is configured to trigger restart if any one, or more, of a pluralitythreshold level conditions are fulfilled.

With reference to FIG. 3, the processing circuit 111 of the constraineddevice 100 may optionally comprise a plurality of processing circuitmodules 301-303 (modules “#1”, “#2”, and “#n”, in FIG. 3). In suchembodiments of the constrained device 100, the restart circuit 121 maybe configured to trigger restart of a first one of the plurality ofprocessing circuit modules 301-303 when the electrical chargeaccumulated by restart circuit 121, in particular by the capacitor Ccomprised in the restart circuit 121, exceeds a first threshold level ofa plurality of threshold levels. Further optionally, the restart circuit121 may be configured to trigger restart of a second one of theplurality of processing circuit modules 301-303 when the accumulatedelectrical charge exceeds a second threshold level of the plurality ofthreshold levels, wherein the second threshold level is preferablydifferent than the first threshold level. It will be appreciated thatembodiments of the invention are not limited to comprising threeprocessing circuit modules 301-303, and the restart circuit 121 beingconfigured with two threshold levels, but may comprise any suitablenumber of processing circuit modules and may be configured with anysuitable number of threshold levels for triggering restart of one ormore corresponding processing circuit modules.

The restart circuit 121 being configured with a plurality of, preferablydifferent, threshold levels is advantageous in that different parts ofthe constrained device 100, in particular different processing circuitmodules 301-303 of the processing circuit 111, may be restartedseparately, and optionally in accordance with a well-defined sequencewhich is determined by the time constant of the restart circuit 121 andthe threshold levels of the restart circuit 121. For instance, and withreference to Eqs. (1), (2), and (4), for a given time constant τ, therestart circuit 121 may be provided with different comparators circuits,as is illustrated in FIG. 3, wherein each comparator circuit isconfigured with a threshold level which is configured so as to triggerrestart of a corresponding processing circuit module 301-303 after adesired duration of time. For instance, the resistors R₁₂ and R₁₃comprised in the comparator circuit #1, and arranged to provide areference voltage to the inverting input of the operational amplifiercomprised in the comparator circuit #1, may be dimensioned to triggerrestart of the processing circuit module #1 after a time which is equalto the time constant τ (e.g., 3 s), and the resistors R₂₂ and R₂₃comprised in the comparator circuit #2, and arranged to provide areference voltage to the inverting input of the operational amplifiercomprised in the comparator circuit #2, may be dimensioned to triggerrestart of the processing circuit module #2 after a time which is longerthen the time constant τ. As an example, according to Eq. (1), after atime t equal to 2·τ, the voltage over the capacitor V_(C) reaches alevel of 0.87·V_(H). With reference to the example describedhereinbefore, the resistors R₁₂ and R₁₃ of the comparator circuit #1 maybe dimensioned with the same values as R₂ and R₃ to trigger restart ofthe processing circuit module #1 after a time which is equal to the timeconstant τ (3 s), and the resistors R₂₂ and R₂₃ may, in accordance withEq. (4), be dimensioned with 1.3 kΩ and 8.7 kΩ, respectively, to triggerrestart of the processing circuit module #2 after a time t equal to 2·τ(6 s).

Embodiments of the constrained device 100 with a processing circuit 111comprising a plurality of processing circuit modules 301-303 and arestart circuit 121 being configured with a plurality of thresholdlevels for separately triggering restart of a corresponding one of theprocessing circuit modules 301-303 is further advantageous in that theyenable restart of only a subset of the processing circuit modules301-303, by discontinuing the transmission of power from the controldevice 200 to the constrained device 100 after one or more of theplurality of processing circuit modules 301-303 have restarted. Thismay, e.g., be achieved by increasing a distance between the two devices100 and 200, or by disabling transmission of power over the NFCair-interface by the control device 200, either by disabling theNFC-interface circuit 215 or the transmission of power by theNFC-interface circuit 215. In this way, and with reference to theexample described hereinbefore, restart of a first one of the processingcircuit modules 301-303, e.g., processing circuit module 301 (module#1), may be achieved after a time which is equal to the time constant τ(3 s), after which transmission of power over the NFC air-interface isdiscontinued. If transmission of power over the NFC air-interfacecontinues after restart of the first processing circuit module 301 hasbeen triggered, the second processing circuit module 302 (module #2) istriggered to restart after harvesting of power by the constrained device100 has commenced for a duration of time which is equal to 2·τ (6 s).

As is illustrated in FIG. 3, the processing circuit 121 may comprise acombination of one or more processing circuit modules 301 and 302 whichare configured to restart in response to receiving a restart signal viaa dedicated reset input of the processing circuit 121, and one or moreprocessing circuit modules (such as module #3) which are not configuredto restart in response to receiving a restart signal via a dedicatedreset input of the processing circuit 121.

The plurality of processing circuit modules 301-303 may, e.g., implementdifferent parts of the functionality of the constrained device 100. Asan example, a first one of the plurality of processing circuit modules301-303 (e.g., module #1) may be operative to perform periodicmeasurements using the sensor 117, whereas a second one of the pluralityof processing circuit modules 301-303 (e.g., module #2) is operative tostore the sensor data 114, and optionally configuration settings whichare used by the constrained device 100, in the memory 112 or any othermemory provided in the constrained device 100. In such scenario, a usercan advantageously first trigger restart of the first processing circuitmodule and subsequently, if restarting the first processing circuitmodule is not sufficient for restoring normal operation of theconstrained device 100, trigger restart of the second processing circuitmodule.

It will further be appreciated that, as an alternative to utilizing asingle charging circuit and a plurality of comparator circuits as isillustrated in FIG. 3, the processing circuit 121 may comprise aplurality of charging circuits which are configured with different timeconstants, which, in combination with a plurality of comparatorcircuits, are configured to separately trigger restart of one or morecorresponding processing circuit modules.

Optionally, the NFC-interface circuit 115 of the constrained device 100may further be configured to trigger restart of the processing circuit111 when a voltage of the harvested power, V_(H), rises above athreshold level after harvesting of power commences (in practice, thisoccurs after the constrained device 100 and the control device 200 havebeen brought into proximity). It will be appreciated that this thresholdlevel is different from the threshold voltage level V_(TH) discussedhereinbefore, and corresponds to a power-on-reset signal which is knownfrom conventional NFC-interface circuits. Such power-on-reset signalsare commonly used to signal that the voltage V_(H) of the harvestedpower is sufficiently high to support an electronic circuit, such as theprocessing circuit 111 or any other electronic circuit comprised in theconstrained device 100, and are typically triggered shortly afterharvesting of power commences, typically within fractions of a secondafter the two devices 100 and 200 have been brought into proximity. Incomparison, triggering restart of the processing circuit 111, or one ormore of the processing circuit modules 301-302 comprised therein, istriggered after a duration of time which is substantially longer.

In the following, and with reference to FIG. 1, embodiments of theNFC-enabled control device 200 are described.

The NFC-enabled control device 200 comprises an NFC-interface circuit215 which is configured to transmit power to an NFC-enabled constraintdevice 100, and to enable exchange of data with the constrained device100, when the constrained device 100 and the control device 200 are inproximity. The control device 200 further comprises a processing circuit211 which is operative to initiate the transmission of power via theNFC-interface circuit 215 to the constrained device 100, and to controlthe exchange of data with the constrained device 100 via theNFC-interface circuit 215. The transmission of power may, e.g., beinitiated in response to detecting proximity of the two devices.Alternatively, the transmission of power may be initiated in response toa user instruction, e.g., the user pressing a button, providing a spokeninstruction or gesture, or based on a configuration setting.

The processing circuit 211 may further be operative to discontinue thetransmission of power to the constrained device 100 when the exchange ofdata with the constrained device 100 is finalized. In this case, theconstrained device 100 is operational and data exchange between thecontrol device 200 and the constrained device 100 commences as expected.The transmission of power is disabled in order to avoid an unintentionalrestart of the constrained device 100, which appears to be functioningand operational. However, the processing circuit 211 may optionally befurther operative to continue the transmission of power to theconstrained device 100 in response to a user instruction, after theexchange of data with the constrained device 100 is finalized. That is,although the constrained device 100 appears to be functional andoperational, and data is exchanged as expected, a user of the controldevice may enforce a restart of the constrained device 100. This may,e.g., be the case if the data which is received from the constraineddevice 100, e.g., sensor data, appears unreliable or erroneous. The userinstruction may, e.g., be the user pressing a button on the controldevice 200, providing a spoken instruction or gesture to the controldevice 200, or changing a configuration setting of the control device200 or a software application or app which the control device 200 isprovided with.

The processing circuit 211 may further be operative to discontinue thetransmission of power to the constrained device 100 in response toreceiving predetermined data from the constrained device 100. That is,the control device 200 stops transmitting power to the constraineddevice 100 in response to the receiving a predetermined signal from theconstrained device 100, similar to an “keepalive” signal. Alternatively,the control device 200 may stop transmitting power to the constraineddevice 100 in response to receiving first data from the constraineddevice 100. This may, e.g., be the case if the constrained device 100has become unresponsive due to a failure, and initiates communication,or responds to an attempt by the control device 200 to initiatecommunication, by transmitting data to the control device 200. If theprocessing circuit 111 of the constrained device 100 comprises aplurality of processing circuit modules 301-303, and the restart circuit121 is configured to trigger restart of one or more of the plurality ofprocessing circuit modules 301-303 when the accumulated electricalcharge exceeds a corresponding threshold level of a plurality ofthreshold levels, the predetermined data may be indicative of which ofthe plurality of processing circuit modules 301-303 has successfullyrestarted, and the control device 200 may stop transmitting power to theconstrained device 100 in response to receiving a signal or data whichis indicative of that one or more processing circuit modules 301-303have restarted, as desired.

The processing circuit 211 may further be operative to discontinue thetransmission of power to the constrained device 100 when thetransmission of power has commenced for a predetermined duration oftime. The duration of time may, e.g., be configured by a user of thecontrol device 200 or by a manufacturer of the constrained device 100.For instance, the predetermined duration of time may be longer than aduration of time required for exchanging data between the control device200 and the constrained device 100 during normal operation, and shorterthan a duration of time required for restarting the constrained device100. In this way, a user of the control device 200 may use the controldevice 200 to perform routine tasks during normal operation, such asretrieving data from the constrained device 100, without the risk ofinadvertently restarting the constrained device 100. As an example, if atypical interaction time is of the order of one second or less, andrestart is triggered after an interaction time of about five or moreseconds, the predetermined duration of time may be set to three seconds.

The NFC-enabled control device 200 may, e.g., be a smartphone, a mobilephone, a tablet, or a portable computer, which is optionally providedwith a dedicated software application or app, or a dedicated controldevice. The software application or app may, e.g., be provided a by amanufacturer of the constrained device 100 so as to enable interactionwith the constrained device 100 using a conventional user device such asa smartphone.

The processing circuit 211 of the control device 200 may comprise one ormore processors, such as Central Processing Units (CPUs),microprocessors, application-specific processors, Graphics ProcessingUnits (GPUs), and Digital Signal Processors (DSPs), or a combinationthereof, and a memory 212 comprising a computer program 213 comprisinginstructions, i.e., a software application or app. The computer program213 is configured, when executed by the processor(s) comprised in theprocessing circuit 211, to cause the NFC-enabled control device 200 toperform in accordance with embodiments of the invention describedherein. The computer program 213 may be downloaded to the memory 212 bymeans of a wireless network interface (not shown in FIG. 1), as a datacarrier signal carrying the computer program 213. The processor(s) mayfurther comprise one or more ASICs, FPGAs, CPLDs, or the like, which incooperation with, or as an alternative to, the computer program 213 areconfigured to cause the NFC-enabled control device 200 to perform inaccordance with embodiments of the invention described herein.

In the following, embodiments of the method 400 of restarting anNFC-enabled constrained device 100 are described with reference to FIG.4. The method 400 is performed by an NFC-enabled control device 200which comprises an NFC-interface circuit 215 which is configured totransmit power to the constrained device 100 and to enable exchange ofdata with the constrained device 100, when the constrained device 100and the control device 200 are in proximity.

The method 400 comprises initiating 401 the transmission of power viathe NFC-interface circuit 215 to the constrained device 100, andcontrolling 402 the exchange of data with the constrained device 100 viathe NFC-interface circuit 215.

The method 400 may further comprise discontinuing 441 the transmissionof power to the constrained device 100 when the exchange of data withthe constrained device 100 is finalized 411. Optionally, thetransmission of power to the constrained device 100 may continue inresponse to a user instruction 412, after the exchange of data with theconstrained device is finalized 411.

The method 400 may further comprise discontinuing 441 the transmissionof power to the constrained device 100 in response to receiving 421predetermined data from the constrained device 100.

The method 400 may further comprise discontinuing 441 the transmissionof power to the constrained device 100 when the transmission of powerhas commenced for a predetermined duration of time 431. Preferably, thepredetermined duration of time is longer than a duration of timerequired for exchanging data between the control device 200 and theconstrained device 100 during normal operation, and shorter than aduration of time required for restarting the constrained device 100.

It will be appreciated that the method 400 may comprise additional,alternative, or modified, steps in accordance with what is describedthroughout this disclosure. An embodiment of the method 400 may beimplemented as a computer program 213 comprising instructions which,when the computer program 213 is executed by one or more processorscomprised in the processing circuit 211, cause the NFC-enabled controldevice 200 to carry out an embodiment of the method 400. The computerprogram 213 may be stored on a computer-readable storage medium 212,such as a memory stick, a RAM, a ROM, a Flash memory, a CDROM, a DVD, orthe like. Alternatively, the computer program 213 may be carried by adata carrier signal, e.g., when the computer program is downloaded tothe NFC-enabled control device 200 via a wireless network interfacecomprised in the NFC-enabled control device 200.

The person skilled in the art realizes that the invention by no means islimited to the embodiments described above. On the contrary, manymodifications and variations are possible within the scope of theappended claims.

1-26. (canceled).
 27. A Near-Field Communication (NFC) -enabledconstrained device comprising: a processing circuit operative toimplement a functionality of the constrained device, an NFC-interfacecircuit configured to harvest power transmitted by an NFC-enabledcontrol device and to enable exchange of data with the control device,when the constrained device and the control device are in proximity, anda restart circuit configured to accumulate electrical charge using theharvested power received from the NFC-interface circuit, and to triggerrestart of the processing circuit when the accumulated electrical chargeexceeds a threshold level.
 28. The constrained device of claim 27, therestart circuit being configured to trigger restart of the processingcircuit after a duration of time, during which harvested power isreceived form the NFC-interface circuit, which is substantially longerthan a duration of time required for exchanging data between the controldevice and the constrained device during normal operation.
 29. Theconstrained device of claim 27, wherein the restart circuit comprises aresistor-capacitor circuit, and wherein the restart circuit isconfigured to trigger restart of the processing circuit when any one, ora combination of, the following conditions are fulfilled: the chargewhich is accumulated by the capacitor rises above a threshold chargelevel, the voltage which builds up over the capacitor rises above athreshold voltage level, and the current through the resistor fallsbelow a threshold current level.
 30. The constrained device of claim 27,the processing circuit comprising a plurality of processing circuitmodules, and the restart circuit being configured to trigger restart ofa first one of the plurality of processing circuit modules when theaccumulated electrical charge exceeds a first threshold level of aplurality of threshold levels.
 31. The constrained device of claim 30,the restart circuit being further configured to trigger restart of asecond one of the plurality of processing circuit modules when theaccumulated electrical charge exceeds a second threshold level of theplurality of threshold levels.
 32. The constrained device of claim 27,further comprising a sensor, the functionality of the constrained devicecomprising reading sensor data from the sensor, storing the sensor datain a memory comprised in the constrained device, and transmitting thesensor data via the NFC-interface circuit to the control device.
 33. Theconstrained device of claim 27, further comprising an actuator, thefunctionality of the constrained device comprising receiving a commandvia the NFC-interface circuit from the control device, and activatingthe actuator in response to the received command.
 34. The constraineddevice of claim 27, being configured to be accessible exclusivelythrough data exchanged via the NFC-interface circuit.
 35. Theconstrained device of claim 27, the NFC-interface circuit being furtherconfigured to trigger restart of the processing circuit when a voltageof the harvested power rises above a threshold level after harvesting ofpower commences.
 36. A Near-Field Communication (NFC)-enabled controldevice for restarting an NFC-enabled constrained device, the controldevice comprising: an NFC-interface circuit configured to transmit powerto the constrained device and to enable exchange of data with theconstrained device, when the constrained device and the control deviceare in proximity, and a processing circuit operative to: initiate thetransmission of power via the NFC-interface circuit to the constraineddevice, and control the exchange of data with the constrained device viathe NFC-interface circuit.
 37. The control device of claim 36, theprocessing circuit being further operative to discontinue thetransmission of power to the constrained device when the exchange ofdata with the constrained device is finalized.
 38. The control device ofclaim 36, the processing circuit being further operative to discontinuethe transmission of power to the constrained device in response toreceiving predetermined data from the constrained device.
 39. Thecontrol device of claim 36, the processing circuit being furtheroperative to discontinue the transmission of power to the constraineddevice when the transmission of power has commenced for a predeterminedduration of time.
 40. The control device of claim 39, wherein thepredetermined duration of time is longer than a duration of timerequired for exchanging data between the control device and theconstrained device during normal operation, and shorter than a durationof time required for restarting the constrained device.
 41. A method ofrestarting a Near-Field Communication (NFC)-enabled constrained device,the method being performed by an NFC-enabled control device comprisingan NFC-interface circuit configured to transmit power to the constraineddevice and to enable exchange of data with the constrained device, whenthe constrained device and the control device are in proximity, themethod comprising: initiating the transmission of power via theNFC-interface circuit to the constrained device, and controlling theexchange of data with the constrained device via the NFC-interfacecircuit.
 42. The method of claim 41, further comprising discontinuingthe transmission of power to the constrained device when the exchange ofdata with the constrained device is finalized.
 43. The method of claim41, further comprising discontinuing the transmission of power to theconstrained device in response to receiving predetermined data from theconstrained device.
 44. The method of claim 41, further comprisingdiscontinuing the transmission of power to the constrained device whenthe transmission of power has commenced for a predetermined duration oftime.
 45. The method of claim 44, wherein the predetermined duration oftime is longer than a duration of time required for exchanging databetween the control device and the constrained device during normaloperation, and shorter than a duration of time required for restartingthe constrained device.
 46. A computer-readable medium comprising,stored thereupon, a computer program comprising computer-executableinstructions for causing an NFC-enabled control device to perform themethod of claim 45, when the computer-executable instructions areexecuted on one or more processors comprised in the control device.